The invention relates to a device for joining all kinds of parts, in particular cores for forming a core assembly, the parts being adapted for insertion into one another with at least one connecting area formed at least in certain regions.
Quite generally, the invention relates to joining all kinds of parts, and to a joining technique, wherein the parts being joined come into mutual surface contact. In most cases, they lie against one another in formfitting engagement, and/or engage one another.
In addition to gluing together the surfaces, it is common to join parts with dowel-type connecting pins. In this connection, it is essential that the parts have suitable recesses, openings, or passages, which are oriented toward one another and in alignment with one another. The connecting pins extend through the recesses, openings, or passages, and are secured therein in force-locking engagement with the parts being joined, thereby interconnecting the parts. Securing of the connecting pins occurs by expansion within the recesses, opening, or passages.
A device of the kind under discussion may also be used, in particular in an advantageous manner, for joining cores into a core assembly, namely in the foundry practice, where for casting all kinds of molded parts, foundry cores or molds are commonly made from separate parts, combined, and joined to a casting mold or a core or mold assembly. These core assemblies are then filled with a molten metal for making, for example, a metallic work piece. In the series production, the core assemblies being filled with the molten metal advance one after the other through a production line.
Core and shell shooting machines for making the cores to be joined have been known from practice for many decades, for example, from DE 31 48 461 C1, which discloses a core and shell shooting machine.
The joining of cores into a core assembly, for example, for casting an engine block, has so far occurred by joining the individual cores by means of screws or tie rods. This is extremely costly because of the manual activity that is required in this instance. Furthermore, it is necessary to eliminate or separate again the screws or tie rods, when removing the cast pieces or when preparing the molding material in this instance mainly sand, including binders.
Furthermore, it is known per se to join cores alternatively with hot-melt adhesives or cold bonding agents. When using hot-melt adhesives, one has to see to it that the kiln temperature be not above the melt point of the hot-melt adhesive during a subsequent passage through a foundry kiln for drying the applied water-based core coating. If so, the adhesive bond would dissolve.
Furthermore, is likewise already known from the prior art to join cores by means of core sand, namely by shooting a so-called key core into hollow spaces provided in the cores being joined, whereby a formfitting engagement is obtained between the respective cores or core parts. This requires a separate shooting operation directly on the already made cores or core parts, which generate quite a considerable expenditure in terms of apparatus.
A device for joining parts, in particular cores for forming a core assembly is also disclosed in DE 197 42 276 A1. This document discloses the use of very special connecting means, namely an expansion body, which is first introduced or inserted with a play into aligning recesses of the parts being joined. In this instance, the expansion body is a so-called expansion element for producing a force-locking engagement between the parts or cores, and one of the recesses is formed in a projection of one of the two parts. The expansion element has the shape of a pin and contains in its wall surface two opposite flats. The expansion element is made of metal, plastic, wood, or even molding sand. For joining the two parts or cores, the expansion element is inserted into the recess provided in one of the two parts. The other part is placed on the projecting portion of the expansion element or slipped on the expansion element. When compressing the cores with their respective front ends by means of a pneumatic or hydraulic device or with a corresponding manipulator, the expansion element spreads, where it has no flats, an annular projection of that part, into which it is inserted. As a result, this part or this projection expands relative to the surrounding wall of the other part, so that a force-locking engagement results between the two engaged parts.
Finally, the known device for joining parts in the manner of a wedge acts in the first place exclusively on two sides upon the areas being expanded, so that as a result of there developing stresses, it is not uncommon that material breakage occurs on the parts being joined. This occurs in particular in such cases, where the parts are brittle, fragile parts, as is the case with cores from molding sand.
It is therefore an object of the present invention to provide a device for joining all kinds of parts, which avoids the risk of damaging brittle or fragile parts to the greatest extent.
The above and other objects are achieved with the present invention by the provision of a clamping member which is provided between the connecting areas of the parts, and which exerts a clamping effect when and as a result of the parts being inserted into one another.
In an advantageous manner, it has been recognized that it is possible to join with simple means all kinds of parts, in particular cores for forming a core assembly, wherein between engageable connecting areas of the parts, a clamping member is provided, which develops a clamping effect during the engagement. The parts are joined to one another solely as a result of being inserted into each other, and while being inserted into one another, namely because of the clamping effect resulting from the clamping member. Accordingly, the connecting areas of the parts are to be adapted to one another in their shape and size such that the clamping member fits inbetween. In the case of a full engagement of the connecting areas, the clamping effect resulting from the clamping member must be adequate.
In an advantageous manner, the connecting areas of the parts being joined to one another are made as male and female portions that fit into one another. In this connection, it is desired that the parts fit into one another at least largely by formfitting engagement. Each clamping member serves as an insert between two connecting areas, so that a clamping effect results, when the connecting areas engage each other. Provided the clamping members being used as inserts are made adequately soft, it will be possible to reduce the clamping force to a minimum, so that damage to the parts is avoided to the greatest extent.
Within the scope of a particularly suitable configuration of the connecting areas, the connecting area of the one part is realized as a cone or frustrum, and the connecting area of the other part as a conical or frustoconical recess. Many other shapes are possible. In this instance, one will always have to make sure that the connecting areas of the parts fit into one another at least largely in a formfitting manner.
If the connecting areas are realized as cones or frustrums and as corresponding recesses, their respective circumferential surface may have different angles. In this connection, it has been shown that in the case of an only extremely small angle of inclination of the circumferential surface, a particularly satisfactory and adequate connection results because of a force-locking engagement. An adaptation to the respective conditions of the parts being joined is possible.
Specifically, the clamping member may be realized such that it is made as a moldable flat layer or sheet, which is adapted for being placed or slipped at least in certain regions onto the connecting area serving as the male portion, and/or for being placed or inserted at least in certain regions into the connecting area serving as the female portion. For example, the sheet could be realized as a closed or open sleeve. Preferably, this sleeve is adapted to the shape of the connecting area. Likewise, it would be possible to realize the sheet or the clamping member as a closed or open ring, which is inserted or slipped at least in certain regions over the connecting area used as the male portion. Both within the scope of a realization as a sleeve and within the scope of a realization as a ring, the clamping member could be open, so that an adaptation to different diameters of the connecting areas is easily possible. At any rate, it is important that with the cooperation of the clamping member, a force-locking engagement results between the connecting areas of the parts being joined. As a result, the parts are interconnected in a gentle manner.
Within the scope of a very particularly advantageous development, it will be of advantage, when the sheet forming the clamping member is adapted for being placed on the free end of the connecting area serving as the male portion, or over the opening of the connecting area serving as the female portion, and adapted for being pulled or pushed in between the connecting areas, when engaging same, until an adequate clamping effect is generated. Insofar, a very simple clamping member would be created, which is pulled into the space between the connecting areas, while engaging the connecting areas. In this connection, a resultant formation of folds will not necessarily interfere. Quite the contrary, such a formation of folds will contribute to the clamping effect, so that a force-locking engagement is attained all around, when the connection areas are engaged.
Within the scope of such a simple embodiment, it will be of further advantage when the sheet is made at least generally circular, and serrated, fringed, or star-shaped in its edge portion. In this respect it is possible to avoid mutual overlapping with an adequately deep incision, so that stress peaks that destroy the parts do just not occur at all. The serrated, fringed, or star-shaped configuration may be realized in that the circular sheet is provided not only with incisions, but that also cutouts are formed, so that the remaining surface of the sheet adapts itself all around between the connecting areas to the surface thereof, without these adapting portions of the layer overlapping one another. Many other configurations or shapes of the clamping members are possible.
To enable a reliable positioning of the clamping member in the form of a flat sheet, in particular within the scope of an overhead installation, or to secure it against an air draft, it would be possible to provide the clamping member or the sheet forming the clamping member with an adhesive. The adhesive would then serve to secure the clamping members to the connecting area forming the male portion. It would also be possible to apply there an adhesive or glue at a later time. Likewise, it is possible that the clamping members or the sheet be inserted or pushed in at least slightly or in part into the connecting area serving as the female portion, so that then occurring frictional forces cause the clamping member to adhere already safely, until the connecting area forming the male portion is finally inserted into the female portion, with the clamping member generating the actual clamping effect between the two connecting areas.
As previously mentioned, it will be of special advantage, when the clamping member is made of a soft material that is at least largely adaptable to the shape of the connecting areas, so that the clamping member adapts itself to all kinds of shapes of the connecting areas. In this connection, the clamping member should be made adequately thick, so as to be able to absorb into itself, during the joining of core assemblies, at least in part, the smallest particles, for example, core sand particles. On the one hand, this measure creates an adequate connection between the parts being joined, and on the other hand, it prevents a xe2x80x9cloose gravel effect,xe2x80x9d which commonly occurs with cores. This effect causes sand to be abraded during the joining of cores, when the cores mutually slide against one another, and it complicates or even precludes, in the form of sand beads, an adequate engagement of the parts. Consequently, the use of the clamping member in accordance with the invention allows a further problem that has arisen until now to be effectively avoided.
In a particularly advantageous manner, the clamping member may be used for compensating increasing wear on molds, namely for maintaining or restoring the required accuracies of fit of male and female portions. In this respect, it is possible to make the clamping member thicker in the case of increasing wear on molds, so that the thicker clamping material is able to restore the necessary accuracy of fit at least to a certain extent. At any rate, it would be possible to use in the case of increasing wear on the molds, increasingly thicker clamping members for compensating problems resulting from wear.
At this point, it should be noted that one can counteract wear of critical mold regions by hard metal inserts, so that yet again a very special function is attached to the clamping members, namely that of avoiding once more or reducing at least the wear on the molds.
The clamping member could be made of cellulose or the like. Within the scope of an especially simple realization, paper or cardboard is used. The costs of such a clamping member may be minimized accordingly.
Further, it is also possible to make the clamping members of plastic or even of a soft metal, depending on the underlying problem. In any case, it is essential that an adaptation in terms of shape to the connecting areas be possible. The use of an adequately soft material should permit a penetration of the smallest particles.
To assist the necessary clamping effect between the connecting areas, it will likewise be of advantage, when the clamping member is configured to be non-smooth on at least one of the two surfaces. Thus, it would be possible to emboss the clamping member or provide it with scales or the like.
Furthermore, it is possible to coat the clamping member on at least one side. Should the material of the clamping member not be adequately soft, one could there provide a soft coating. Likewise, it would be possible to use as coating an adhesive, so that the particles can be bonded initially by the adhesive. In this instance, the coating of adhesive could realize an adhesive bond in addition to the actual clamping effect.
Within the scope of a particularly refined development, the material of the clamping member could be a material of the kind which expands in a defined manner. Thus, one could use, for example, a material that expands at certain temperatures or certain air humidities, so that a repeated clamping of the parts occurs by a subsequent expansion of the clamping member only in the engaged state of the connecting areas, or in addition to the clamping effect developing during the engagement.